This application is based upon, and claims the benefit of priority of, prior Japanese Patent Application 2001-133279, filed on Apr. 27, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection valve operated by an electromagnetic force.
2. Description of Related Art
Recently, in general, fuel injection valves having high output, low noise, and the like are in demand. Furthermore, it is desired that the fuel injection valves consume low fuel amounts (i.e. are economical), and conform to strict exhaust-gas emission regulations as they apply to gasoline and diesel engines. Thereby, engine fuel supply may be accurately performed by a fuel injection valve.
In fuel injection valves, a fixed connector (fixed core) and a movable core connected to a valve body are contained in a cylindrical pipe. A solenoid coil is provided at an outer circumferential location relative to them, and the fixed connector and the movable core form a part of a magnetic circuit. When the solenoid coil is energized and generates a magneto motive force, a magnetic path is formed from the fixed connector to the movable core. Then, the movable core is attracted to the fixed connector by an electromagnetic force, and the valve body opens a fuel injection hole. When the energization for the solenoid coil is stopped, the movable core detaches (moves away) from the fixed connector by a spring (force applying member), and the valve body closes the fuel injection hole. The fuel injection valve is controlled by an engine control unit (ECU), and it is generally controlled by adjusting a voltage applied to the solenoid coil. An opening-closing time and opening-closing timing are controlled for the valve body, so that an injection amount of fuel and injection timing thereof, injected into an intake pipe (rail) and cylinders, are accurately controlled.
However, improving the response performance of the valve body for opening and closing the fuel injection hole is required to accurately control such a fuel injection system. Accurately controlling the fuel injection system is effective at improving the response performance which increases an attracting force that attracts the movable core. When an electromagnetic force is increased by increasing the number of turns of the solenoid coil or current supplied to the solenoid coil, the attracting force is increased. However, the fuel injection valve size or power consumption, usually, must also increase. Further, a design change may be required which leads to increased production costs.
The present invention has been made in view of the above problems. That is, an electromagnetic force, generated between the fixed connector and the movable core, can be efficiently used. It is an object of the present invention to provide a fuel injection valve which can improve response performance of a valve body, for example, by increasing an attracting force of the movable core.
In JP-W-H11-500509, the following fuel injection valve is disclosed. A movable core is inserted into a cylindrical pipe, and a fixed connector (fixed core), having a larger diameter than the movable core, faces, or is adjacent to, the movable core. In a conventional fuel injection valve, generally an outer diameter of the fixed connector is larger than that of the movable core as in the fuel injection valve disclosed in JP-W-H11-500509, or both are equal in size to each other. The reason is as follows. When magnetic flux is generated in a direction from an end surface (fixed action surface) of the fixed connector to an end surface (movable action surface) of the movable core, the greater an area of the fixed action surface, the larger the attracting force obtained.
The above problems have been studied and tests were conducted to reveal the following result which may be contrary to conventional common sense. That is, when the outer diameter of the fixed action surface is made smaller than that of the movable action surface, the attracting force generated therebetween is increased. So, the present invention has been made.
A fuel injection valve according to the present invention includes a cylindrical pipe, a fixed connector inserted into and fixed to the pipe, a movable core inserted into the pipe so as to slide in contact with an inner circumferential surface thereof, a solenoid coil energized by a power supply source, and a valve body being movable together with the movable core. The fixed connector has a fixed action surface at one end side and is made of a magnetic material. The movable core has a movable action surface facing the fixed action surface at one end and is made of a magnetic material. The solenoid coil generates magnetic flux transmitted from the fixed action surface to the movable action surface, and it generates an attracting force between the fixed connector and the movable core. The valve body opens and closes a fuel injection hole by energizing and de-energizing the solenoid coil. In the fuel injection valve, an outer diameter of the fixed action surface is smaller than that of the movable action surface.
In the fuel injection valve, when the magnetic flux is transmitted from the fixed action surface to the movable action surface and a magnetic circuit is formed from the fixed connector to the movable core, the following result occurs. That is, when the outer diameter of the fixed action surface is smaller than that of the movable action surface, the attracting force generated therebetween is increased.
In the fuel injection valve using this result, for example, the attracting force between the fixed connector and the movable core can be increased while a size of the solenoid coil or an applied voltage (current) is not increased. Thus, response performance of opening and closing the valve body can be improved. In the fuel injection valve according to the present invention, when the attracting force and the response performance is the same as in a conventional case, the size of the solenoid coil and associated power consumption can be reduced. The reason for this result can be considered in the following manner.
That is, as in a conventional fuel injection valve, when the outer diameter of the fixed action surface is larger than that of the movable action surface, the magnetic flux around an outer circumferential portion is transmitted from the fixed action surface to the movable action surface in a fashion or direction not substantially perpendicular to the movable action surface, but in a direction inclined to the movable action surface. Therefore, a vertical component (a component in a normal line direction of the action surfaces) of the electromagnetic force generated around the outer circumferential portion is reduced. This vertical component is transformed to the attracting force required to attract the movable core in an axial direction. Accordingly, when an angle at which the magnetic flux around the outer circumferential portion is transmitted to the movable action surface is altered from 90 degrees, an effectively transformed amount from the electromagnetic force to the attracting force is reduced, so that the attracting force is ultimately reduced.
In the fuel injection valve according to the present invention, since the outer diameter of the fixed action surface is smaller than that of the movable action surface, the magnetic flux can be readily transmitted from the fixed action surface to the movable action surface substantially in a direction or fashion perpendicular to the movable action surface. The electromagnetic force acting between the fixed action surface and the movable action surface can be effectively transformed to the attracting force for the movable core. Especially, magnetic flux density around the outer circumferential portion is large. Therefore, as the magnetic flux around the outer circumferential portion is transmitted to the movable action surface substantially in a direction perpendicular to the movable action surface, the attracting force increases.
Additionally, the magnetic flux around the outer circumferential portion is transmitted to the movable action surface substantially in a direction perpendicular to the movable action surface, thereby aligning the magnetic flux at the center portion. That is, the magnetic flux at the center portion can also be readily transmitted to the movable action surface in a substantially vertical direction (referencing FIG. 2). Thus, the electromagnetic force acting between the fixed action surface and the movable action surface can be further efficiently used as an effective attracting force for the movable core. Accordingly, the larger attracting force acts on the movable core than in a conventional case.
The response performance of the movable core, that is, of the valve body is improved by this increase in the attracting force. Therefore, a minimum injection amount can be suitably controlled, and the fuel injection valve can be more accurately controlled.
In the present invention, the important areas are not the outer diameters of the fixed connector and the movable core, but the outer diameters of the fixed action surface and the movable action surface which face each other. That is, the outer diameter of the fixed connector is not necessarily required to be smaller than that of the movable core. For example, the outer diameter of the fixed action surface can be made smaller than that of the movable action surface by de-burring an outer circumferential portion (end) of the fixed connector. Dents and burrs can be prevented from being generated on the fixed connector by performing the de-burring, and quality control can be also readily performed.
Here, when the outer diameter of the fixed action surface is made excessively smaller, an effective area where the electromagnetic force acts is reduced, and the attracting force may then also be reduced. Therefore, preferably, the outer diameter (d1) of the fixed action surface is made smaller than that (d2) of the movable action surface by 0.5-10% of the outer diameter of the movable action surface. That is, (d2xe2x88x92d1)/d2=0.005xe2x88x920.1
When smaller than 0.5%, both outer diameters are substantially equal to each other. When larger than 10%, the attracting force is reduced. 2.5-3.5%, 2-5%, 1-7% are preferred in this order (e.g., 2.5-3.5% is more preferable than 2-5%). The fuel injection valve according to the present invention is substantially for a solenoid fuel injection valve. However, it is applicable to a gasoline engine or a diesel engine, and is for injecting fuel into a cylinder or an intake manifold.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for to purposes of illustration only and are not intended to limit the scope of the invention.